The blow molding of hollow articles of glass is well known in the art, and is usually carried out by the blow and blow, or, the press blow processes, either in hot molds or pasted molds, which also are well known in the art.
Such forming processes involve three stages:
1. Working of the preform (by blowing or pressing). PA1 2. Thermal homogenization (by superheating or re-heating). PA1 3. Blowing and cooling (setting or cooling out). PA1 (a) Heat transfer from the glass to the blow air. PA1 (b) Heat transfer from the glass to the finishing mold. PA1 (c) Heat transfer from the glass to atmosphere. PA1 (d) Heat transfer from the glass to the damp paste. PA1 1. Greater capacity in the removal of heat. PA1 2. Increased speed in the removal of heat. PA1 3. A more uniform and effective action in the removal of heat. PA1 4. Greater simplicity in the design of the blowing head. PA1 5. Ease of installation and control. PA1 6. Reduction in the number of components of the mold, as compared with present systems. PA1 7. The elimination of relative movement between members of the mold. PA1 8. Longer useful life of the mechanical parts. PA1 9. A reduction in, or elimination of maintenance.
Product quality and production speed depend mainly on the blowing and cooling stage, this stage being the one that takes the most time to complete.
Two operations are carried out during the blowing and cooling stage: the first is to shape the article by inflating it in the finishing mold, and the second is to remove heat from the molded article and cause setting thereof within the mold.
Of the operations mentioned above, the removal of heat from the molded articles is the more time consuming, and in turn determines the total time required in the blowing and cooling stage.
When heat is removed from the molded glass articles, the following heat transfer phenomena take place:
From analysis of the aforesaid phenomena, it is apparent that the major problem to be resolved is the acceleration of heat transfer to the four elements heretofore recited.
A previous attempt to accelerate heat transfer from molded articles of glass to blow air is described in the U.S. Pat. No. 2,123,145. This patent teaches the introduction of a conduit into the interior of the molded article, in order to introduce blow air at the bottom thereof. This is done hermetically, at first, so as to blow form the article, and is then continued allowing air to escape from the molded article to cool the article.
In this system, the introduction of the tube into the article further increases the time required in the operation. Also, the volume of blow air is insufficient to remove heat from the mold at a rate permitting a considerable reduction of the time required in the forming cycle. Moreover, the mechanical components thereof are complicated, and require precise adjustment for their effective functioning.
Another attempt for achieving the aforesaid purpose is described in U.S. Pat. No. 4,339,258, which relates to the of blowing hollow glass articles in pasted-mold-machines. This patent teaches the positioning of a blowing nozzle in alignment with, but in a non-sealed relation to a neck ring. A space is left between the blow head and the upper neck ring, thus permitting the blow air to get into the article and continuously exit from the interior of the ware through said space. The article is thus molded in a manner which permits a reduction in the time required for forming and cooling the ware.
Several laboratory tests were carried out in order to determine the parameters of the method cited above. It was found that, notwithstanding the great improvement in the rate of forming and cooling of glass articles over the past methods and apparatus, the desired optimum cooling was not attained. Air entering directly into the molded article, formed a pressurized air chamber within its interior, which in turn hampered air from flowing to the bottom of the article, thus diminishing the rate of heat removal from the molded article.